Add features and fix some bugs in remind.coffee

- Adds support for "hubot remind me on <date/time> to <action>"
- Requires new npm packages:
  - moment, for duration/time formatting
  - lodash, for utility functions
  - chrono-node, for parsing natural language type dates (e.g. next Tuesday, Tomorrow at 3:00pm, etc.)
- Adds "hubot delete reminder <action>" command
- Adds "hubot show reminders" command
- Fixes some bugs